1Z0-811 Java Basics and Syntax Practice Test 4 — 15 Questions

Question 1

What is the output?

```java
public class Test {
    public static void main(String[] args) {
        String s1 = "hello";
        String s2 = "hello";
        System.out.println(s1.equals(s2));
    }
}
```

Accepted Answer

True. The code compares two String objects 's1' and 's2' using the equals() method. Since both strings have the same content "hello", equals() returns true. The System.out.println statement then prints 'True'.

Answer

No output

Answer

Compilation error

Answer

False

Question 2

You are developing a Java application for a library management system. The system must track the number of books in each genre. You need to store genre names (String) and their counts (int). The data will be accessed frequently and modified rarely. Which Java data structure should you use to store this mapping efficiently, while ensuring that genre names are unique?

Accepted Answer

HashMap. HashMap is the correct choice because it stores key-value pairs, where each genre name (String) is a unique key mapped to its count (Integer). This provides O(1) average-time complexity for lookups and updates, which is ideal for frequent access and rare modifications. The HashMap ensures key uniqueness via its hash-based implementation, directly meeting the requirement of unique genre names.

Answer

ArrayList<Book>

Answer

LinkedList<String>

Answer

HashSet<String>

Question 3

You are writing a program that processes a list of transactions. Each transaction has a timestamp (long), amount (double), and type (String). The program needs to iterate through the transactions in the order they were added. Which collection should you use to maintain insertion order and allow fast iteration?

Accepted Answer

ArrayList<Transaction>. ArrayList maintains insertion order and provides O(1) random access and fast iteration via index-based traversal. It is the correct choice when you need to preserve the order in which elements were added and iterate over them sequentially without requiring sorting or unique constraints.

Answer

TreeSet<Transaction>

Answer

LinkedList<Transaction>

Answer

HashSet<Transaction>

Question 4

Arrange the steps to declare and initialize a one-dimensional array in Java in the correct order.

Accepted Answer

Step 1: Declare array variable (e.g., int[] arr;), Step 2: Allocate memory using new keyword (e.g., arr = new int[5];), Step 3: Assign values to elements (e.g., arr[0] = 1; arr[1] = 2; ...).. The process involves declaring the array variable, then assigning it a new array or initializer, and optionally providing initial values.

Answer

Step 1: Allocate memory using new keyword, Step 2: Declare array variable, Step 3: Assign values.

Answer

Step 1: Assign values to elements, Step 2: Declare array variable, Step 3: Allocate memory.

Answer

Step 1: Declare array variable, Step 2: Assign values to elements, Step 3: Allocate memory.

Question 5

Arrange the steps to use the Scanner class to read user input in Java in the correct order.

Accepted Answer

1. Import java.util.Scanner; 2. Create Scanner object: Scanner sc = new Scanner(System.in); 3. Prompt user: System.out.print("Enter value: "); 4. Read input: String input = sc.nextLine(); 5. Close scanner: sc.close();. First import Scanner, then create an instance, prompt user, read input, and finally close the scanner.

Answer

1. Create Scanner object: Scanner sc = new Scanner(System.in); 2. Import java.util.Scanner; 3. Prompt user: System.out.print("Enter value: "); 4. Read input: String input = sc.nextLine(); 5. Close scanner: sc.close();

Answer

1. Import java.util.Scanner; 2. Prompt user: System.out.print("Enter value: "); 3. Create Scanner object: Scanner sc = new Scanner(System.in); 4. Read input: String input = sc.nextLine(); 5. Close scanner: sc.close();

Answer

1. Import java.util.Scanner; 2. Create Scanner object: Scanner sc = new Scanner(System.in); 3. Read input: String input = sc.nextLine(); 4. Close scanner: sc.close(); 5. Prompt user: System.out.print("Enter value: ");

Question 6

Match each access modifier to its visibility level.

Accepted Answer

private: Visible only within the same class. In Java, access modifiers control visibility: private (class-only), default (package), protected (package + subclasses), public (everywhere). Common mistakes include confusing private with default and protected with private.

Answer

private: Visible within the same package

Answer

protected: Visible only within the same class

Question 7

Match each Java collection interface to its characteristics.

Accepted Answer

List: Ordered collection (also known as sequence) that allows duplicate elements.. List is ordered and allows duplicates; Set is unordered and no duplicates; Queue is FIFO order; Map maps keys to values with unique keys. Common confusions include swapping List/Set characteristics or misidentifying Map as a collection of single elements.

Answer

Set: Ordered collection that allows duplicate elements.

Answer

Map: Collection of elements with no order and no duplicates.

Question 8

A class defines a static variable initialized at declaration: static int count = 10;. A static method attempts to modify it: count = 20;. Which statement is true?

Accepted Answer

The variable can be changed to 20. Static variables belong to the class, not instances, and can be accessed and modified by static methods. The assignment `count = 20;` is valid and changes the value from 10 to 20 at runtime.

Answer

The variable cannot be accessed from a static method

Answer

The code causes a compilation error

Answer

The variable is read-only

Question 9

A developer uses a switch statement with a String variable. Which is true about this usage?

Accepted Answer

It works with strings starting from Java 7. Starting from Java 7 (JSR 334), the switch statement supports String objects in addition to primitive types and enums. The compiler uses the `hashCode()` and `equals()` methods of the String class to evaluate the switch expression against case labels, making it a valid and efficient way to branch on string values.

Answer

It works only with primitive types

Answer

It causes a compilation error because strings are not supported

Answer

It requires a default case

Question 10

Which loop construct guarantees that the loop body executes at least once?

Accepted Answer

do-while loop. The do-while loop is the only Java loop construct that guarantees the loop body executes at least once because the condition is evaluated after the body executes. In contrast, the while and for loops evaluate the condition before the first iteration, so the body may never execute if the condition is initially false. The enhanced for loop also checks for elements before entering the body.

Answer

Enhanced for loop

Answer

while loop

Answer

for loop

Question 11

A method receives an int parameter and modifies its value inside the method. Does this change affect the caller's argument?

Accepted Answer

No, because Java passes a copy of the value. Java uses pass-by-value for all parameters. When an int is passed to a method, a copy of the value is made, so modifications inside the method affect only the copy, not the original variable in the caller's scope.

Answer

No, unless the parameter is marked as volatile

Answer

Yes, because the parameter is an int

Answer

Yes, because Java passes a reference

Question 12

Given int[] arr = {1,2,3}; which correctly creates a new array with length 5 and copies the contents of arr?

Accepted Answer

int[] newArr = Arrays.copyOf(arr, 5);. `Arrays.copyOf(int[] original, int newLength)` creates a new array of the specified length (5) and copies the elements from the original array into it, padding with default values (0 for int) for any extra positions. This method is specifically designed for this task, ensuring the original array remains unchanged.

Answer

int[] newArr = new int[5]; newArr = arr;

Answer

int[] newArr = arr.clone(); newArr.length = 5;

Answer

int[] newArr = Arrays.copy(arr, 5);

Question 13

A class defines two methods with the same name but different parameter lists. This is known as:

Accepted Answer

Method overloading. Method overloading occurs when a class defines multiple methods with the same name but different parameter lists (different number, type, or order of parameters). This is a compile-time polymorphism mechanism in Java that allows a method to handle different inputs without changing its name.

Answer

Method overriding

Answer

Method hiding

Answer

Method shadowing

Question 14

Which access modifier allows members to be accessed only by classes in the same package?

Accepted Answer

default (no modifier). In Java, the default (package-private) access modifier, which is applied when no explicit modifier is used, restricts member access to only classes within the same package. This is the only access level that provides package-level visibility without inheritance or subclass access.

Answer

protected

Answer

private

Answer

public

Question 15

A subclass overrides a method from its superclass. Which annotation should be used to indicate the overriding intention?

Accepted Answer

The @Override annotation is optional but recommended. The @Override annotation is optional in Java; the compiler will still enforce method overriding without it. However, it is strongly recommended because it provides a compile-time check that the method correctly overrides a superclass method, preventing accidental overloading or typos in the method signature.

Answer

The @Override annotation is not allowed

Answer

The @Override annotation is used for overloading

Answer

The @Override annotation is mandatory